This invention relates to an electronic circuit device and a method of producing the same which improves the reliability of the joints between an electronic circuit part such as a semiconductor chip or a part and a circuit substrate, by mechanical or thermo-mechanical treatment solder with high-melting-point solder (or wrought solder), the solder being subjected to a process which will be described later, and heat treatment.
In the field of electronic circuit devices, so called "surface mounting" methods have been adopted in order to protect semiconductors or parts mechanically and chemically and to improve the productivity and reliability of electronic circuit devices. Among these, a method of connecting a semiconductor chip 1 and the peripheral end surface of a substrate 2 which faces the semiconductor 1 by minute solder 3 through electrodes 4 and 5, as shown in FIG. 1, is known as the mounting method with the highest density (cf. U.S. Pat. No. 3,871,014, or Japanese Patent Publication No. 28735/1968). In these methods, the chip 1 and the circuit substrate 2 are connected using the effect of the wetting and diffusion of the completely melted solder 3 with respect to the electrodes 4 and 5. Since it is necessary to melt the solder completely, segregation of the alloy structure, defects, and residual stress disadvantageously often result during the cooling stage of the solder, so that the solder 3 has a cast structure with low elongation. The solder 3 which have these cast structures have low elongation with respect to external force, producing nonuniform deformation, which leads to the serious problem of the solder 3 being fractured by various kinds of stresses produced during use in a comparatively short period of time due to metal fatigue of the solder 3.
Such a problem of soldering interconnection has become more important with the increasing tendency towards miniaturization of electronic parts and increase in mounting density as in the case of LSI.